Both Luther and Calvin came to their positions from intense personal inner struggle. Both had originally been clerics of the Catholic Church; Luther had been a German professor, Calvin a French lawyer and humanist. Luther's writings were in response to the corruption that was prevalent in the Catholic Church, primarily the sale of indulgences; Calvin responded to his own inner conviction of the utter depravity of man.
Luther said that salvation comes from faith alone; the Pope had no special authority; rather he spoke of the "priesthood of all believers." Luther argued that there were only three sacraments as opposed to the seven practiced by the church; those in which Jesus actually participated while on earth.
Calvin frequently spoke of the “abyss” over which mankind hovered. The most important element of his theology was the doctrine of predestination. Calvin wrote that God was sublime, and so overwhelming and awe-inspiring that human beings were insignificant, sinful, and unworthy. Yet God was also a God of love, who planned from the beginning of the universe to the end of time, and selected some human beings, the “elect,” for salvation; others were selected for damnation. The following quote is from Calvin:
Predestination we call the eternal decree of God by which He determined in Himself what would have to become of every individual of mankind. For they are not all created with a similar destiny; but eternal life is foreordained for some and eternal damnation for others. Every person, therefore, being created for one or the other of these two ends, we say is predestined to life or to death.
Predestination was the area in which Luther and Calvin disagreed most. Where Luther had emphasized reconciliation to God through faith, Calvin emphasized obedience to His will. Calvin’s position on the Eucharist also differed with Luther. He argued that there was a “spiritual” presence. There was such a close connection between the communion host and the gift of salvation which it symbolizes that one can
“easily pass from one to the other. For why should the Lord put in your hand the symbol of his body unless it was to assure you that you really participate in it?”
Luther's teaching was of consubstantiation: Christ was present at the Eucharist, but the bread and wine were not transformed, as had been taught by the Catholic Church.